Wire coating extruder

ABSTRACT

The screw extruder serves to form a coating on welding electrodes and comprises a feed hopper, two feeder screws, which are disposed in the feed hopper and mesh with a backlash, a precompacting screw, which is disposed below the feed hopper, a first housing surrounding said precompacting screw, two highpressure screws, which mesh substantially without backlash, and a second housing surrounding said two high-pressure screws. Said feeder screws are operable to deliver coating composition to said precompacting screw and the latter is operable to deliver coating composition to said two high-pressure screws.

Un ted States Patent 91 [11] 3,802,385

Strohmeier Apr. 9, 1974 WIRE COATING EXTRUDER [56] References Cited [75]Inventor: Harald Strohmeier, Kapfenberg, UNITED STATES PATENTS Austria798,606 9/1905 Hawkins 118/405 3,216,375 1l/l965 Ernst 259/41 1Asslgneei Gebr- B0111" Q- AG, 3,467,743 9/1969 Otani 425/205 KapfenbergAusma 3,563,514 2/1971 Shattuck 425/205 22 Pl d: Ma 6 1973 1 16 rPrimary ExaminerMorris Kaplan 1 PP 338,575 Attorney, Agent, orFirm-Holman 8L Stern Related US. Application Data 57 ABSTRACT [62]Division of Ser. No. 112,384, Feb. 3, 1971. Pat. No. 1

3734472- The screw extruder serves to form a coating on weldingelectrodes and comprises a feed hopper, two 30 Foreign Applicationpriority Data feeder screws, which are disposed in the feed hopper Feb 01970 Austria 001174 and mesh with a backlash, a precompacting screw,I970 Austria 001172 which is disposed below the feed hopper, a firsthousing surrounding said precompacting screw, two high- [52] U S Cl118/405 pressure screws, which mesh substantially without [51] In} .0hose 3/12 backlash and a second housing surrounding Said two [58] Fie'ld"H' high-pressure screws. Said feeder screws are operable to delivercoating composition to said precompacting screw and the latter isoperable to deliver coating composition to said two high-pressurescrews.

3 Claims, 3 Drawing Figures 1 1 WIRE COATING EXTRUDER This is adivisional of application Ser. No. ll2,384, filed Feb. 3, 1971, now US.Pat. No. 3,734,472.

This invention relates to a screw extruder for forming the coatings ofwelding electrodes, which extruder comprises extruder screws arranged inthree seriesconnected stages.

Apparatus are known in which the high pressures which are required toform the coatings of welding electrodes are produced in the coatingcompositions by means of pistons moving in cylinders. These apparatusare operated intermittently and for this reason may be used to coatwelding wires only at relatively low rates.

To avoid that disadvantage it has also been proposed to use screwextruders to form such coatings. The known screw extruders cannotsubject the coating compositions to pressures which are sufficienttoform satisfactory coatings on welding electrodes.

It is an object of the invention to avoid the stated disadvantages andto provide a screw extruder which enables a trouble-free application ofvery high pressures of at least several hundred yatmospheres to coatingcompositions for welding electrodes and a continuous forcing of saidcompositions into a die in which the desired coating is formed on thewelding wire, which is supplied at high speed. In a screw extruder ofthe kind mentioned first hereinbefore, this is accomplished according tothe invention in that two feeder screws are provided in a feed hopperand mesh with a backlash and are succeeded by a precompacting screw,which is disposed below the feed hopper and surrounded by a housing, andsaid precompacting screw is succeeded by two high-pressure screws, whichmesh substantially without backlash and are enclosed by a commonhousing. This ensures that the very tough coating composition will beforced into the precompacting screw and will be conveyed by the same ifthe precompacting screw is disposed closely below the feed hopper andthe axis of symmetry between the two feeder screws intersects in knownmanner the longitudinal axis of the precompacting screw.

An embodiment of the screw extruder according to g the invention isshown diagrammatically and by way of example in the drawing, in whichFIG. 1 is a vertical longitudinal sectional view showing a screwextruder for forcing a coating on welding electrodes,

FIG. 2 is a partly sectional top plan view showing the same screwextruder,

FIG. 3 is a horizontal sectional fragmentary view showing on an enlargedscale the delivery end of said screw extruder viewed from above.

A downwardly tapering feed hopper 1 comprises two feeder screws 2, whichmesh with a large backlash and adr driven in mutually opposite sensesand positively connected by two gears 3. One feeder screw 2 is directlycoupled to the stub shaft 5 of an electric gearmotor 4, which is securedto the support 6 of the feed hopper 1. The other feeder screw 2 isrotatably mounted in a bearing 7, which is carried by the support 6. Thefeeder screws 2 receive the coating composition and force it through anopening 8 in the feed hopper 1 into a precompacting screw 10, which isdisposed directly below the hopper 1 and driven by an electric gearmotor12. The axis of symmetry disposed between the two feeder screws 2intersects the longitudinal axis of the precompacting screw 10. Theprecompacting screw 10 is closely surrounded by a housing 9. The lead sof the precompacting screw 10 and the channel crosssection of said screwdecrease toward the delivery end of the screw 10. As a result, thecoating composition is fed under an increased pressure into the twohigh-pressure screws 14, which are desirably mounted a small distancebeside the delivery end 11 of the precompacting screw 10. Theprecompacting screw and the housing surrounding it may have a conicaltaper toward the outlet end. The high-pressure screws 14 driven inmutually opposite senses mesh substantially without backlash and areclosely surrounded by a common housing 13. They are also positivelyconnected by two gears 15 and are driven by an electric gearmotor 16. Anapproximately funnel-shaped wire feeder 17 is provided beyond thedelivery end of the high-pressure screws 14 between their geometricallongitudinal axes a-b and extends into the housing 13. The geometriclongitudinal axes a-b of the high-pressure screws 14 and the geometriclongitudinal axis c-e of the wire feeder 17 include obtuse angles a. Thehousing 13 carries a die 18, which is spaced from and concentric withthe wire feeder l7 and has an inside diameter D, which is much largerthan the outlet diameter of the wire feeder 17. The welding wire 19 isfed through that die 18 continuously and at a high speed and during thismovement is centered by the wire feeder 17. The coating compositioncharged into the feeder hopper l is fed by the feeder screws 2 disposedin the feed hopper ll into the precompacting screw 10 and by the latterinto the highpressure screws 14. The coating composition which leavesthe high-pressure screws 14 under very high pressure passes through thedie 18 and emerges from the same into the open together with the weldingwire 19. In this way, the desired coating 20 is formed on the weldingwire 19.

Compared to the known apparatus mentioned above, the screw extruderaccording to the invention has the advantage of permitting the formationof satisfactory coatings on welding electrodes in a continuous operationand at very high speed.

What is claimed is:

1. A screw extruder for forming a coating on welding electrodes, saidscrew extruder comprising a feed hopper,

two feeder screws, which are disposed in the feed hopper and mesh with abacklash,

a precompacting screw, which is disposed below the feed hopper,

a first housing surrounding said precompacting screw,

two high-pressure screws, which mesh substantially without backlash, and

a second housing surrounding said two high-pressure screws,

, said feeder screws being operable to deliver coating composition tosaid precompacting screw and the latter being operable to delivercoating composition to said two high-pressure screws,

each of said high-pressure screws having a delivery end and definingageom etrical longitudinal axis,

a wire feeder defining a peripherally closed passage being disposedbetween said geometrical longitudinal axes, and

said second housing carrying an extrusion die, which is spaced from andconcentric with said wire and adapted to receive wire from said wirefeeder and said passage is defined by a tube. coating composition fromthe delivery ends of said 3. A screw extruder as set forth in claim 3,in which high-pressure screws. said passage is defined by afunnel-shaped member.

2. A screw extruder as set forth in claim 5, in which

1. A screw extruder for forming a coating on welding electrodes, saidscrew extruder comprising a feed hopper, two feeder screws, which aredisposed in the feed hopper and mesh with a backlash, a precompactingscrew, which is disposed below the feed hopper, a first housingsurrounding said precompacting screw, two high-pressure screws, whichmesh substantially without backlash, and a second housing surroundingsaid two high-pressure screws, ,said feeder screws being operable todeliver coating composition to said precompacting screw and the latterbeing operable to deliver coating composition to said two highpressurescrews, each of said high-pressure screws having a delivery end anddefining a geometrical longitudinal axis, a wire feeder defining aperipherally closed passage being disposed between said geometricallongitudinal axes, and said second housing carrying an extrusion die,which is spaced from and concentric with said wire and adapted toreceive wire from said wire feeder and coating composition from thedelivery ends of said high-pressure screws.
 2. A screw extruder as setforth in claim 1, in which said passage is defined by a tube.
 3. A screwextruder as seT forth in claim 1, in which said passage is defined by afunnel-shaped member.